Effects of acute hypoxia on cerebral and muscle oxygenation during incremental exercise

• Published in: Journal of applied physiology (1985) Vol. 103; no. 1; pp. 177 - 183
• Main Authors: Subudhi, Andrew W, Dimmen, Andrew C, Roach, Robert C
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.07.2007; American Physiological Society
• Subjects: Acclimatization; Acute Disease; Adult; Altitude; Biological and medical sciences; Blood Volume; Cerebral Cortex - blood supply; Cerebral Cortex - metabolism; Cerebral Cortex - physiopathology; Cerebrovascular Circulation; Cross-Over Studies; Effects; Exercise; Fatigue; Fundamental and applied biological sciences. Psychology; Hemoglobins - metabolism; Humans; Hypoxia; Hypoxia - blood; Hypoxia - metabolism; Hypoxia - physiopathology; Male; Muscle Contraction; Muscle Fatigue; Muscular system; Oxygen - blood; Oxygen - metabolism; Oxygen Consumption; Oxyhemoglobins - metabolism; Physical Endurance; Pulmonary Ventilation; Quadriceps Muscle - blood supply; Quadriceps Muscle - metabolism; Quadriceps Muscle - physiopathology; Reproducibility of Results; Single-Blind Method; Spectroscopy, Near-Infrared; Spectrum analysis; Physical exercise; Oxygen; near-infrared spectroscopy; Acute; Central nervous system; Environmental factor; Fatigue; Striated muscle; Encephalon; Vertebrata; Mammalia; Hypoxia; Oxygenation; Altitude
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01460.2006

University of Colorado Altitude Research Center, Denver Health Science Center and Colorado Springs Campuses, Colorado Submitted 29 December 2006 ; accepted in final form 11 April 2007 To determine if fatigue at maximal aerobic power output was associated with a critical decrease in cerebral oxygenation, 13 male cyclists performed incremental maximal exercise tests (25 W/min ramp) under normoxic (Norm: 21% F I O 2 ) and acute hypoxic (Hypox: 12% F I O 2 ) conditions. Near-infrared spectroscopy (NIRS) was used to monitor concentration (µM) changes of oxy- and deoxyhemoglobin ( [O 2 Hb], [HHb]) in the left vastus lateralis muscle and frontal cerebral cortex. Changes in total Hb were calculated ( [THb] = [O 2 Hb] + [HHb]) and used as an index of change in regional blood volume. Repeated-measures ANOVA were performed across treatments and work rates ( = 0.05). During Norm, cerebral oxygenation rose between 25 and 75% peak power output {Power peak ; increased (inc) [O 2 Hb], inc. [HHb], inc. [THb]}, but fell from 75 to 100% Power peak {decreased (dec) [O 2 Hb], inc. [HHb], no change [THb]}. In contrast, during Hypox, cerebral oxygenation dropped progressively across all work rates (dec. [O 2 Hb], inc. [HHb]), whereas [THb] again rose up to 75% Power peak and remained constant thereafter. Changes in cerebral oxygenation during Hypox were larger than Norm. In muscle, oxygenation decreased progressively throughout exercise in both Norm and Hypox (dec. [O 2 Hb], inc. [HHb], inc. [THb]), although [O 2 Hb] was unchanged between 75 and 100% Power peak . Changes in muscle oxygenation were also greater in Hypox compared with Norm. On the basis of these findings, it is unlikely that changes in cerebral oxygenation limit incremental exercise performance in normoxia, yet it is possible that such changes play a more pivotal role in hypoxia. near-infrared spectroscopy; fatigue; altitude Address for reprint requests and other correspondence: A. W. Subudhi, Dept. of Biology, Univ. of Colorado at Colorado Springs, 1420 Austin Bluffs Parkway, Colorado Springs, CO 80918 (e-mail: asubudhi{at}uccs.edu )